Catalytic hydrocyanation systems, particularly pertaining to the hydrocyanation of olefins, are known in the art. For example, liquid phase systems useful for the hydrocyanation of butadiene to form pentenenitriles (PN) are known in the art. For example, Drinkard, U.S. Pat. No. 3,496,215, discloses the hydrocyanation of butadiene using nickel catalysts with monodentate phosphite ligands. As used in this patent, and as will be used herein, the term "pentenenitrile" is intended to mean cyanobutene. Likewise, "butenenitrile" means cyanopropene. Bidentate phosphite ligands complexed to zero-valent nickel and platinum are known to be useful in the liquid phase hydrocyanation of butadiene, as described by Baker et al., J Chem. Soc., Chem. Commun., 1991, 803-804.
The pentenenitriles so formed are subjected to further hydrocyanation and/or isomerization to form adiponitrile (ADN), a commercially important material in the manufacture of nylon. For example, Drinkard, U.S. Pat. No. 3,536,748, discloses the liquid phase isomerization of 2-methyl-3-butenenitrile in the presence of a zero valent nickel complex and Chia, U.S. Pat. No. 3,676,481, discloses an improvement additionally utilizing tri(hydrocarbyl)boron promoters.
The hydrocyanation of activated olefins such as conjugated olefins (e.g., butadiene and styrene) and strained olefins (e.g., norbornene) proceeds without the use of a Lewis acid promoter, while hydrocyanation of unactivated olefins such as 1-octene and 3-pentenenitrile normally require the use of a Lewis acid promoter. Teachings regarding the use of a promoter in the hydrocyanation reaction appear, for example, in U.S. Pat. No. 3,496,217.
Certain multidentate phosphite ligands useful in the present invention for the hydrocyanation of diolefins have been used for the hydrocyanation of monoolefins. Commonly assigned, WO 95/14659 and U.S. Pat. No. 5,512,696, disclose bidentate phosphite ligands preferably used in combination with a Lewis acid promotor to hydrocyanate monoolefins.
The present invention provides for an improved process for the hydrocyanation of diolefinic compounds, such as butadiene, and isomerization of nonconjugated acyclic nitrites without the need for Lewis acid promoters utilizing zero-valent nickel and a multidentate phosphite ligand. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description of the invention which hereinafter follows.